Climate change and groundwater resources in Mekong Delta, Vietnam

Journal of Groundwater Science and Engineering

Vol.4 Vol.5 No.2 No.1 Jun. Mar. 2016 2017

Climate change and groundwater resources in Mekong Delta, Vietnam Duong D Bui1*, Nghia C Nguyen1, Nuong T Bui 2, Anh T T Le3, Dao T Le1 1

National Center for Water Resources Planning and Investigation, MONRE, Vietnam. 2 Tokyo Metropolitan University, Japan. 3 Center for Environmental Fluid Dynamics, Hanoi University of Science, Vietnam.

Abstract: Groundwater resources have considerable influences on the human population and socioeconomic development of Vietnam and the Mekong River Delta (MRD). This paper presents an overview of the relationship between climate change and groundwater in the MRD, including the challenges, strategies and technical measures. Our results showed that groundwater levels are related to other climate and hydrological variables (i.e., rainfall, river levels, etc.); therefore, the impacts of climate change on the groundwater resources of the Mekong delta are significant, especially on groundwater recharge. Based on the results of this study, it is recommended that groundwater development in the future should focus on reducing groundwater harvesting, enhancing groundwater quantity by establishing artificial works and exploiting surface water. This study suggests that the Artificial Neural Network (ANN) model is an effective tool for forecasting groundwater levels in periods of 1 month and 3 months for aquifers in the natural and tidal regime areas of the delta. Keywords: Groundwater management; Climate change; ANN model; Mekong River Delta

1 Introduction 1.1 Status of groundwater Groundwater resources have considerable influences on the human population and socioeconomic development of Vietnam, particularly in the Mekong River Delta (MRD) region; however, few studies have focused on the trends in the impacts of climate change on groundwater resources. Scientists believe that climate change will have the greatest effect on water resources, agriculture, food security, community health and coastal zones. These issues require both short-term and long-term solutions to improve the planning and management of groundwater resources with regard to future climate change scenarios. The main objective of this study is to provide information on groundwater exploitation and suggest strategies to improve the management of

this valuable resource under the threat of climate change. The MRD has eight aquifers (Holocene (qh); Upper Pleistocene (qp3); Upper-Middle Pleistocene (qp2-3); Lower Pleistocene (qp1); Middle Pliocene (n22); Lower Pliocene (n21); Upper Miocene (n13); Upper-Middle Miocene (n12-3) and Bazan Kanoizoi and Paleozoic–Mesozoic, which are two fissure and fissure-pore aquifers. Generally, the aquifer system in the MRD has an artesian basin structure and the lithology of each aquifer consists of fine to coarse sand, gravel, and pebbles. The deepest area of the basement is located below the Tien and Hau Rivers and rises to the NE, N and NW borders. The characteristics of the aquifers in the MRD are summarized in Table 1. Approximately 2 million wells supply groundwater more than 2.8 million m3/day, thus, groundwater is important for the socioeconomic development of South Vietnam.

*

Corresponding author. E-mail: [email protected]

76 76

http://gwse.iheg.org.cn


1.2 Predicted climate change scenarios In 2012, the Vietnam Ministry of Natural Resources and Environment (MONRE) projected climate change and sea level rise scenarios for

Vol.4 No.1 No.2 Mar. Jun. 2016 Vol.5 2017

Vietnam according to low (B1), average (B2) and high (A2) carbon dioxide emission scenarios. These carbon dioxide emission scenarios are described as follows.

Fig. 1 Location map of the MRD (Google Earth and Vuong B T, 2014) Table 1 Characteristics of the main aquifers in the MRD Aquifers

Distribution

Holocene (qh)

40.000 km

Thickness Depth Materials Types (m) (m) 15.5 16.9 Fine Non-pressure

Broadly Upper Pleistocene distributed over (qp3) the area

29.1

47.9

UpperBroadly Middle distributed over Pleistocene the area (qp2-3)

41.5

86.8

Lower Broadly Pleistocene distributed over (qp1) the area

38.1

146.5

Broadly Middle 2 distributed over Pliocene (n2 ) the area

51.3

206.5

Broadly Lower 1 distributed over Pliocene (n2 ) the area

53.78

274.8

Bazan Kanoizoi PaleozoicMesozoic

80 NW


4

Groundwater potential Poor

From poor to Silty clay, average, suitable for clay, sand, Low pressure residential gravels exploitation High potential, Silty clay, suitable for clay, sand, Low pressure small-scale gravels pumpings Silty clay, clay, sand, Average From average to pebble, pressure high gravels Courtyard mixed sand, Rich groundwater High pressure clay-silty potential sand Courtyard Poor to rich mixed sand, groundwater High pressure clay-silty potential sand Poor to average Non or local bazan olivin potential pressure groundwater

Groundwater quality Low quality Mainly salty

Good quality

Good quality

Good quality

Good quality

Local pressure

77 77

78

n22

n21

5

6

94 537

302

8 911

4 517

Q(m3/ng)

SL(well)

Q(m3/ng)

SL(well)

877

SL(well)

0

0

662

34 185

2

SL(well)

Q(m3/ng)

SL(well)

Q(m3/ng)

SL(well)

0

SL(well)

Q(m /day)

48

14

SL(well)

3

0

Q(m /ng)

3

864

Q(m /ng)

3

8 856

Q(m /ng)

3

41 673

Q(m /ng)

3

6 374

Number of wells

Aquifer

An Giang

0

0

0

0

0

0

12 465

24

61 838

18 688

174 319

74 644

106

12

0

0

248 728

93 368

Bac Lieu


78

Note: SL: Number of wells; Q: Exploitation flow

ms

qp1

4

8

qp2-3

3

n13

qp3

2

7

qh

1

Total

No.

Province

Vol.4 No.2 Jun. 2016

0

0

3 300

5

10 161

23

0

0

0

0

541

204

1 926

548

2 059

1 873

17 986

2 653

Ben Tre

0

0

0

0

433

304

105 198

42 353

28 592

8 535

24 895

16 135

0

0

0

0

159 118

67 328

Ca Mau

0

0

0

0

0

0

41 972

105

0

0

146 872

48 693

0

0

0

0

188 844

48 798

Can Tho

0

0

0

0

0

0

114 743

1 181

0

0

1 426

3 657

0

0

0

0

116 169

4 838

Đong Thap

0

0

0

0

0

0

0

0

7 328

2 113

43 234

28 638

11 982

9 821

0

0

62 544

40 572

Hau Giang

0

0

0

0

3 500

3

6 835

35

3 642

2 090

149 032

72 297

34 018

18 283

414

422

197 441

93 130

Kien Giang

0

0

3 869

54

35 609

1 356

144 585

1 998

11 491

26

0

0

0

0

0

0

195 554

3 435

Long An

Table 2 Current groundwater exploitation in 13 local provinces in the MRD


0

0

11 314

85

0

0

0

4

17 186

2 814

189 241

65 311

25 240

11 051

1 869

804

244 850

80 069

Soc Trang

0

0

0

0

0

0

0

0

0

0

220 175

84 362

0

0

4 598

4 471

224 773

88 833

Tra Vinh

0

0

0

0

13 550

16

0

0

0

0

18 923

22 191

0

0

0

0

32 473

22 207

Vinh Long


0

0

99 752

842

23 536

378

17 376

310

0

0

0

0

0

0

0

0

140 664

1 530

Tien Giang

Journal of Groundwater Science and Engineering Vol.5 No.1 Mar. 2017



Fig. 2 Typical hydrogeological cross-section of the Nam Bo Basin from Tuyen Chau Thanh (Kien Giang) to Phu Giao (Binh Duong)

The projected temperature scenarios are as follows: -B1 scenario: In the dry seasons, the average temperature is projected to increase by 0.9-1.2 °C (by 2050); and 1.0-1.7 °C (by 2100). In rainy seasons, average temperature is projected to increase by 1.1-1.5 °C (by 2050); and 1.5-2.0 °C (by 2100). -B2 scenario: In the dry seasons, the average temperature is projected to increase by 0.8-1.3 °C (by 2050); and 1.5-2.0 °C (by 2100). In the rainy seasons, the average temperature is projected to increase by 1.2-1.6 °C (by 2050); and 2.5-3.8 °C (by 2100). -A2 scenario: In the dry seasons, the average temperature is projected to increase by 0.9-1.4 °C (by 2050); and 1.9 to 3.3 °C (by 2100). In the rainy seasons, average temperature is projected to increase by 1.2-1.6 °C (by 2050); and 2.5-3.8 °C (by 2100). The projected precipitation scenarios are as follows: -B1 scenario: The rainfall in the dry seasons will decrease by 2.1-7.1% (by 2050) and 2.8-9.9% (by 2100). The rainfall in the rainy seasons will increase by 1.4-7.7% (by 2050) and 1.9-10.5% (by 2100). -B2 scenario: The rainfall in the dry seasons is projected to decrease by 2.3-7.8% (by 2050) and 4.3-15.1% (by 2100). The rainfall in the rainy seasons is projected to increase by 1.5-8.3% (by 2050) and 3.0-15.9% (by 2100). -A2 scenario: The rainfall in the dry seasons will decrease by 2.4-8.3% (by 2050) and 5.5-19.3% (by 2100). The rainfall in the rainy http://gwse.iheg.org.cn

seasons is projected to increase by 1.6-8.8% (by 2050) and 3.7-20.2% (by 2100). The projected sea level rise scenarios are as follows: -B1 scenario: In the east, the sea level will rise between 22 and 26 cm (by 2050) and 51-66 cm (by 2100). In the west, the sea level will rise between 24 and 28 cm (by 2050) and 52-72 cm (by 2100). -B2 scenario: In the east, the sea level will rise between 23 and 27 cm (by 2050) and 59-75 cm (by 2100). In the west, the sea level will rise between 25 and 30 cm (by 2050) and 62-82 cm (by 2100). -A2 scenario: In the east, the sea level will rise between 26 and 30 cm (by 2050) and 79-99 cm (by 2100). In the west, the sea level will rise between 28 and 32 cm (by 2050) and 85-105 cm (by 2100).

2 Climate change and groundwater sustainability 2.1 Climate change and hydrologic variability 2.1.1 Rainfall The southern delta of Vietnam experiences rainfall ranging from 1 400 mm to 2 200 mm. Rainfall tends to increase gradually from a northeast to southwest direction. The amount of rainfall is 2 400 mm in Ca Mau Province. The annual average rainfall is approximately 1 800 mm. Higher average rainfall occurs in the upper and 79 79

Journal of Groundwater Science and Engineering middle of the Dong Nai, La Nga and Be rivers (2 400-2 800 mm), the west coast region of the Mekong Delta (2 200-2 400 mm), the downstream of the Dong Nai River and the upstream of the Saigon River (2 000-2 200 mm). The lower average rainfalls occurs in the downstream of the

Vol.4 Vol.5 No.2 No.1 Jun. Mar. 2016 2017 Vam Co River and left bank area of the Tien River ( 0.9. This result indicates that the

Vol.4 Vol.5 No.2 No.1 Jun. Mar. 2016 2017 ANN model with the network structure and parameters defined above provides accurate forecast results and thus can be used to forecast the groundwater levels for natural and tidal regime areas of the Middle Pliocene aquifer (n22) of the southern delta region with prediction times from 1 to 3 months.

Table 5 Calibration and validation parameters of the ANN model for the natural and tidal regime areas of Middle Pliocene aquifer (n22) in the southern delta Regime areas

Forecast times 1 month

Natural 3 months 1 month Tidal 3 months

Cases Calibration Validation Calibration Validation Calibration Validation Calibration Validation

Model Structure 17-12-1 14-10-1 12-9-1 18-12-1

Study parameter

Moment parameter

RMSE

Good pattern (%)

0.1

0.5

0.04

100

0.1

0.5

0.018

90

0.15

0.45

0.02

100

0.15

0.45

0.01

95

0.2

0.5

0.04

100

0.2

0.5

0.03

95.8

0.3

0.5

0.002

100

0.3

0.5

0.009

93

1 month

3 months

Fig. 10 Results of the groundwater level forecasts for 1 month and 3 month periods for natural regime 2 areas in the Middle Pliocene aquifer (n2 )

88 88



4 Conclusions The paper provides a comprehensive overview of the interactions between climate change and groundwater in the Mekong delta. The study shows that groundwater levels are correlated with climate and hydrological variables (i.e., rainfall, river levels, etc.), and climate change has an especially significant impact on groundwater recharge in the Mekong Delta. The results illustrated that the impacts of groundwater exploitation and climate change on the groundwater resources in the Mekong Delta could be qualified by groundwater


flow modelling and diffusion modelling. In addition, the results also indicate that the ANN model is an effective tool for forecasting groundwater levels over periods of 1 month and 3 months for the natural and tidal regime of the Pliocene aquifers of the delta. To develop effective adaption and management strategies for the groundwater in the Mekong Delta under climate change, a number of strategies, actions and technical measures must be enacted. Groundwater development in the future should focus on reducing groundwater harvesting, enhancing groundwater quality via additional artificial works, and exploiting surface water to a greater degree.

1 month

3 months

Fig. 11 Results of the groundwater level forecasts for 1 month and 3 month periods for the tidal regime 2 area in the Middle Pliocene aquifer (n2 )

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